This invention relates to vane type air pumps, and more particularly it deals with a vane type air pump suitable for use in injecting secondary air into engine exhaust passages for additional burning of the exhaust gases emitted from the engine combustion chambers to reduce the proportion of unburned exhaust gas constituents.
In one type of air pump known in the art, vane members are mounted for rotation through needle bearings on a pivot shaft in loose fitting, so that the vane members can move axially relatively easily. In this construction, when axially directed loads are produced in the vane members, the vane members would be moved by such loads and the contact pressure between the vane members and side seal members would increase, thereby causing great wear on the side seal members. In the initial stages of development of such wear, gaps between the side seal members and vane members would increase in size and cause a reduction in the flow rate of air supplied by the pump. A further increase in the wear of the seal members would result in the vane members coming into contact with one end of a cylinder portion of the housing. When this situation is brought about, the vane members would strike and end of the cylinder portion and make a noise as they rotate, in addition to the reduction in the flow rate of air delivered by the pump. The noise makes the user feel unpleasant because it is generated by metal-to-metal contact.